The invention relates to a cylinder head of an internal-combustion engine having a divided carrier for receiving camshafts which act upon valves by way of bucket tappets, the carrier having bearings for the camshafts constructed to be detachable from the cylinder head housing and having longitudinal webs extending in the direction of the crankshaft in parallel and at a distance from one another and having transverse webs extending at a right angle with respect to the longitudinal webs.
From the German Patent Document DE-36 41 129 Cl, a camshaft bearing frame is known for an in-line internal-combustion engine having four valves for each cylinder. This camshaft bearing frame is screwed onto the basic housing of the cylinder head as a separate part. This bearing frame comprises a cast part which has webs extending between the cylinders and at the two ends of the cylinder head transversely with respect to the longitudinal direction as well as two webs which extend in parallel in the longitudinal direction and rest on the lateral housing walls of the cylinder head. In the transversely extending webs, lower bearing half-shells are developed for the bearings of camshafts, the upper halves of which bearings are formed by bearing caps which are separated from one another and can be screwed onto the camshaft bearing frame. This bearing frame permits a separate pre-assembly of the camshafts with their bearings. This construction has the disadvantage that, despite the separate camshaft bearing arrangement, an expensively constructed cylinder head housing remains which has undercuts, for example, as a result of the receiving devices for the bucket tappets arranged in it and thus can be cast only with a broken core. The resulting structure and the surface are not optimal with respect to stability.
In the German Patent Document DE 38 19 655, a four-valve cylinder head is disclosed for an internal-combustion engine in which the receiving devices for the bucket tappets are combined in pairs in the manner of spectacles. This cylinder head has a complicated shaping which requires a sand casting procedure because of the many undercuts on the cover side opposite the combustion chamber side. This process requires a thorough and time-consuming cleaning of the cover side after the casting.
It is an object of the invention to provide a cylinder head of high rigidity for a internal-combustion engine which avoids the above-mentioned disadvantages and thus makes it possible to manufacture this cylinder head in a simple casting process. In addition, it must be possible to mount this cylinder head mechanically.
This object is achieved by providing a arrangement wherein the carrier has struts extending as longitudinal webs, the struts being formed of receiving devices for the bucket tappets and bridges connecting these receiving devices. Additional characteristics which develop the invention advantageously are contained in the subclaims.
It is a particular advantage of this invention that the camshaft bearing arrangement as well as the receiving devices serving the guiding of the bucket tappets are removed from the cylinder head housing. As a result, the bottom side facing the combustion chamber and the cylinder head cover side disposed opposite this bottom side, because of their simple shaping, can be manufactured in a common casting process, for example, a chill casting process. The resulting cast structure has high homogeneity and improved material parameters in comparison to the known solutions. As a result, the danger of crack formations in the cylinder head housing is reduced considerably.
Independently of the cylinder head housing, the carrier can be manufactured in the diecasting process and can then be machined in a cost-effective manner. The upper and lower part of the carrier each comprise parts of a center web as well as parts of several transverse webs. For the stiffening of the transverse webs, no separate weight-increasing longitudinal webs are arranged in the carrier; on the contrary, this function is taken over by struts which extend on both sides of the center web in the lower part of the carrier and comprise receiving devices guiding bucket tappets, these receiving devices being connected with one another by way of bridges. Each receiving device, in turn, by way of at least one support, is supported on the part of the center web extending in the lower part of the carrier. In the case of a preferred application in an internal-combustion engine having two inlet and two outlet valves respectively for each cylinder, the receiving devices of a cylinder which are used for the bucket tappet bearing and interact in pairs are connected with one another by way of a bridge constructed as a rib, while the bridge between receiving devices belonging to adjacent cylinders is constructed as lower bearing parts of bearings for two camshafts. Thus a light-weight stiff carrier is obtained, the struts of which, as a result of their design, contribute to the stiffening of the carrier and act as a bearing for bucket tappets.
In another embodiment of the invention the receiving devices of a cylinder which interact in pairs are connected by way of a bridge constructed as a lower bearing part of a bearing of a camshaft, the bridge between receiving devices pertaining to adjacent cylinders being connected by way of a bridge constructed as a rib.
In both embodiments of the invention, the center web widens above each cylinder in a ring-shaped manner to form at least one ring element. The passage openings formed by the ring elements permit the mounting of a spark plug or of an injection device. In another embodiment having two ring elements above each cylinder, for example, a dual ignition can be realized, in this case, two valves being preferably arranged for each cylinder.
In all embodiments of the invention, the contour of the upper part of the carrier is adapted to that of the lower part of the carrier; i.e., it carries a corresponding number of ring elements in the center web, and the upper bearing parts for the bearings of the camshafts are, in each case, arranged above the bridges of the lower part of the carrier constructed as the lower bearing part. For a further stiffening of the carrier, stiffening ribs may be arranged in the upper part of the carrier between the transverse webs. It may therefore be used advantageously in self-igniting as well as in spark-ignited internal-combustion engines with two or more valves for each cylinder as well as in the case of a single or dual arrangement of spark plugs.
Another important advantage is the fact that the invention results in considerable freedoms in the case of the valve position with respect to the combustion chamber as well as in the case of the arrangement of the cylinder head bolts. In the case of a internal-combustion engine having, for example, four valves for each cylinder which are arranged spherically with respect to the combustion chamber, the requirement of a stressable and easily accessible arrangement of the cylinder head screws while bucket tappet guides are arranged in the cylinder head housing and the simultaneous requirement of a minimal constructional length of the internal-combustion engine must not be met. It is only the removal of the camshaft bearing and of the bucket tappets according to the invention which permits a free accessibility to the bores in the cylinder head housing which serve the passage opening of the cylinder head bolts and permits a stressable arrangement of these bores in areas of maximal stability of the cylinder block disposed underneath.
The cylinder head mounting first requires the inserting of the valves into the cylinder head housing and the mounting of the cylinder head bolts. Then the valve springs as well as the valve disks are mounted. Subsequently, either the completely pre-assembled carrier can be screwed onto the cylinder head housing as a complete unit or its individual components can be mounted successively. In the latter case, the lower part of the carrier is inserted first and the bucket tappets are guided into the receiving devices. Subsequently the camshafts are inserted and the upper part of the carrier is screwed onto the lower part of the carrier and the whole carrier is screwed onto the cylinder head housing.
The carrier can be completely mounted mechanically and subsequently can be mechanically mounted on the cylinder head housing.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.